The placement of tubes and catheters in biological tissue is generally accomplished by a blind technique utilizing anatomical landmarks for guidance. Despite strict adherence to protocol the catheter, or tube, may deviate from the desired pathway for many different reasons, some of which are within the control of the technician and some that are not.
Methods and techniques for access to the central venous system have been well established. Hemodynamic monitoring and infusion of hyperosmolar solutions and irritating drugs requires the positioning of the catheter tip most commonly in the superior vena cava and less commonly in the inferior vena cava. Aberrant positioning of the catheter and catheter tip, either on insertion or by spontaneous migration thereafter, may result in morbid complications including venous or arterial thrombosis, pericardial tamponade, retrograde cerebral perfusion with neurotoxic symtomatology, venous perforation with thoracic or mediastinal cavity perfusion, and arrhythmias.
Gastric or intestinal positioning of various tubes are also frequently placed by a blind approach. Malposition of these tubes may result in severe consequence as well.
Current practice dictates visualization of catheters or tubes during or following insertion by radiograph or fluoroscopy. Most commonly the radiograph is taken following catheter placement to confirm proper positioning of the device, the tip in particular. Spontaneous migration can presently only be determined by repeated radiograph or fluoroscopy. Repeated exposure of the patient and medical personnel to irradiation is undesirable and costly. In addition, it is often inconvenient to move a patient to an x-ray facility or bring a portable x-ray unit to the patient either in the hospital or home, and may result in prolonging initiation of therapy.
Catheter tip-finding devices now in service can only locate the catheter tip at the time of insertion of the catheter by using a specially instrumented guidewire, however, no system is available which can trace a catheter's location after insertion. An example of such a device is disclosed in U.S. Pat. No. 4,905,698 issue Mar. 6, 1990, and assigned to Pharmacia Deltec Inc. of St. Paul, Minn. In the Pharmacia device the catheter is inserted with a guide wire mounted internal to the catheter. A part of the guidewire is a magnetic coil pick-up device at the distal end of the guidewire located within the distal end of the catheter. Once the guidewire/catheter combination is in place and the technician is assured that it is in the correct location, the guidewire is removed. To use the catheter of the Pharmacia design the guidewire must first be removed. By so doing the ability to locate the end of the catheter by the magnetic method of Pharmacia is no longer possible since the magnetic pick-up device for locating the end of the catheter is attached to the distal end of the guidewire.
It would be advantageous to not only be able to locate the tip of a placement guidewire upon insertion of the guidewire/catheter combination, but to also be able to determine the full length position upon insertion, and equally important is the ability to continually be able to monitor the location of the catheter at any time thereafter in a diagnostic manner. The later function is particularly desirable since there is no assurance that the catheter will not migrate to another location while it is still in use because of physical movements of the patient. In addition, no device is presently available which can locate the position of implanted port mounted catheters. It is important to note that tubes (such as enteral feeding tubes) inserted into the body are physically very similar to catheters and it would be advantageous to have a diagnostic location capability for them upon insertion as well as after the fact since they too can become malpositioned. The present invention clearly has all of these capabilities.